Tom Ripley lives in a shabby brownstone in New York City and works as a casual extortionist when he meets Herbert Greenleaf. Herbert, the father of Tom’s onetime acquaintance Dickie Greenleaf, is desperate for Dickie to return from Europe, where he’s living as a painter in a small Italian village called Mongibello. Herbert offers to pay Tom’s way if Tom will travel to Europe and convince Dickie to come home. Tom, who grew up poor and who remains envious of the lifestyles of the wealthy people he meets in New York, accepts the offer and boards a boat bound for Europe.
In Italy, Tom orchestrates a casual run-in with Dickie. Dickie and Marge Sherwood are the only two Americans in Mongibello, and Tom, though sensing a strained sexual tension between the two of them, attempts to embed himself into their world. At first, Dickie is cold and standoffish. However, Tom confesses to Dickie that he’s been sent by Herbert, and Dickie, amused by Herbert’s desperation, accepts Tom as a friend. Together, the two travel around Italy, and become incredibly close. Tom moves into Dickie’s home, and Dickie lends Tom his clothes and even calls him “Mr. Greenleaf” jokingly. Marge, upset and perturbed by the two men’s sudden closeness, confronts Dickie, and Dickie’s coolness toward Tom returns. Tom, realizing that his luxurious and carefree existence in Italy may be coming to an end, decides to murder Dickie and assume his identity. As a gifted forger and impersonator, Tom believes that the feat will be a simple one. On a trip to San Remo, Tom and Dickie take a boat out into the bay and, while they are at sea, Tom kills Dickie by striking him with an oar and sinking his body. After sinking the boat, Tom returns to shore and begins to cover up his crime and take the steps needed to become Dickie Greenleaf.
Tom absconds to Rome, where he slightly changes his appearance, rents an apartment under Dickie’s name, and spends Dickie’s money. He wears Dickie’s clothes and expensive rings, and luxuriates in his decadent new life. He writes letters to Marge, explaining that he has had to move away and cannot see her in order to figure out his feelings toward her, and to Dickie’s parents, explaining his decision to remain in Italy after all. When another American, Freddie Miles, obtains “Dickie’s” address and arrives for a visit, Tom answers the door as himself and narrowly avoids being found out, though Freddie is suspicious—after all, Tom is dressed in Dickie’s clothes and is wearing Dickie’s jewelry. Tom puts Freddie off, assuring him that Dickie is just downstairs at a nearby café, but, on his way out, Freddie encounters “Dickie’s” landlady, who insists that “Signor Greenleaf” is the only resident of the apartment and is, in fact, right upstairs. When Freddie returns to investigate, Tom murders him as well, and, after staging a scene of drunken revelry, drives Freddie’s body out to a cemetery and abandons it behind a headstone.
When the police discover Freddie’s body, they question “Dickie,” believing unquestioningly that he his who he says he is. Tom is relieved, but soon encounters a newspaper headline which describes the discovery of a bloodstained boat in the San Remo bay. Realizing that if a body is found in the water as well it will be assumed to be that of Tom Ripley—since Tom has been living as Dickie and has left no trail of his “own” whereabouts—and “Dickie Greenleaf” will be a suspect in not just one but two murders—that of Freddie Miles, and that of Tom Ripley. Marge arrives in town, and Tom speaks to her over the phone as himself, assuring her that everything is all right, before leaving for Sicily as Dickie in order to abandon the trail of Dickie’s identity there and return to Italy as Tom Ripley. After several days of “behaving” once again as Tom Ripley, he sends two suitcases of Dickie’s belongings ahead to Venice, in case he wants to claim them sometime in the future, and returns to Rome as himself. When he does, the newspapers describe the search for a “missing” Dickie Greenleaf. A search ensues, and garners more and more attention in the Italian press. Tom moves to Venice, where he attends parties and fields questions as to Dickie’s whereabouts. Soon, Marge arrives in town, and, after spotting Dickie’s rings in Tom’s apartment, comes to the conclusion that Dickie must have committed suicide—he would never, she insists, be without his rings. Herbert arrives in Italy as well, with an American investigator, but “Dickie’s” trail has gone cold. Tom, in one brazen, final act of deceit, composes a letter from “Dickie” which bequeaths his entire estate unto Tom. Though nervous to go through with such a huge endeavor, Tom forwards the letter to Herbert, then embarks on a journey to Greece. However, after the discovery of Dickie’s trunks at the American Express in Venice, Tom fears that he will be found out when the authorities obtain his fingerprints. Upon docking in Greece, Tom notices policemen on the shore, and is sure that his streak of luck and deceit has run out. However, the police do not stop him when he disembarks the ship. Confused, Tom heads to the American Express to collect his mail—a letter from Herbert has arrived, acquiescing to “Dickie’s” wishes that Tom be the sole inheritor of his estate and confirming that the funds will be transferred to Tom shortly. Relieved, Tom hails a cab, and instructs the driver to take him to the finest hotel in town.